Recessed lead leadframe packages

ABSTRACT

Leadframes for semiconductor packages. Implementations may include a plurality of leads extending inwardly into an opening surrounded by the plurality of leads where the plurality of leads except for at least one are configured to mechanically couple at a surface of a semiconductor chip. The at least one of the plurality of leads that is not configured to mechanically coupled at the surface of the semiconductor chip be configured to electrically couple with the semiconductor chip

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of the earlier U.S. Utilitypatent application to Ricodeau entitled “Recessed Lead LeadframePackages,” application Ser. No. 14/800,881, filed Jul. 16, 2015, nowpending, the disclosure of which is hereby incorporated entirely hereinby reference.

BACKGROUND

1. Technical Field

Aspects of this document relate generally to leadframes, such asstructures and devices used in packaging semiconductor chips.

2. Background Art

Leadframes are used to make electrical connections between a silicon dieof semiconductor package and an electronic circuit board or printedcircuit board (PCB). Various leadframes include leads that aremechanical structures that extend through a mold material or otherpackaging material/structure enclosing the semiconductor chip thatconnect electrical pads or connectors on the semiconductor die withcorresponding electrical pads or connectors on the electrical circuitboard. For various package types, the leadframe supports the die duringwire bonding and during molding of package/mold compound around the die.

SUMMARY

Implementations of leadframes may include: a plurality of leadsextending inwardly into an opening surrounded by the plurality of leadswhere the plurality of leads except for at least one are configured tomechanically couple at a surface of a semiconductor chip. The at leastone of the plurality of leads that is not configured to mechanicallycoupled at the surface of the semiconductor chip may include a thinnedportion adjacent to the semiconductor chip (thinned lead) and may beconfigured to electrically coupled with the semiconductor chip.

Implementations of leadframes may include one, all, or any of thefollowing:

The thinned portion of the thinned lead may be half etched.

The thinned lead may be configured to carry a high voltage signal to thesemiconductor chip.

The plurality of leads may be configured to mechanically support thesemiconductor chip through coupling at the surface of the semiconductorchip through a die bonding material.

The thinned lead may not be mechanically coupled at the surface of thesemiconductor chip through the die bonding material.

The plurality of leads may be configured to couple with an electroniccircuit board at a surface of each of the plurality of leads oppositethe surface of the semiconductor chip.

A perimeter of the surface of each of the plurality of leads oppositethe surface of the semiconductor chip may be smaller than a perimeter ofa surface of each of the plurality of leads that is configured to becoupled at the surface of the semiconductor chip.

The surface of each of the plurality of leads except for the thinnedlead opposite the surface of the semiconductor chip may be half etched.

Implementations of a chip-on-lead package may include a leadframecoupled to a semiconductor chip where the leadframe includes a pluralityof leads extending inwardly into an opening surrounded by the pluralityof leads. At least one of the plurality of leads may include a thinnedportion adjacent to the semiconductor chip (thinned lead). The thinnedlead may electrically couple with a high voltage connector of thesemiconductor chip. The plurality of leads, except for the thinned lead,may mechanically couple to the semiconductor chip through a die bondingmaterial.

Implementations of a chip-on-lead package may include one, all, or anyof the following:

The thinned portion of the thinned lead may be half etched.

The plurality of leads may be configured to couple with an electroniccircuit board at a surface of each of the plurality of leads oppositethe surface of the semiconductor chip.

A perimeter of the surface of each of the plurality of leads oppositethe surface of the semiconductor chip except for the thinned lead may besmaller than a perimeter of a surface of each of the plurality of leadsconfigured to be coupled at the surface of the semiconductor chip.

The surface of each of the plurality of leads except for the thinnedlead opposite the surface of the semiconductor chip may be half etched.

Implementations of a chip-on-lead package may include a leadframecoupled to a semiconductor chip where the leadframe includes a pluralityof leads extending inwardly into an opening surrounded by the pluralityof leads. At least one of the plurality of leads may electrically couplewith a high voltage connector of the semiconductor chip and does notmechanically couple at a surface of the semiconductor chip through a diebonding material.

Implementations of chip-on-lead packages may include one, all, or any ofthe following:

The at least one of the plurality of leads that electrically coupleswith the high voltage connector may include a thinned portion.

The thinned portion may be half etched.

The foregoing and other aspects, features, and advantages will beapparent to those artisans of ordinary skill in the art from theDESCRIPTION and DRAWINGS, and from the CLAIMS.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations will hereinafter be described in conjunction with theappended drawings, where like designations denote like elements, and:

FIG. 1 is a top view of a conventional chip-on-lead package with moldcompound surrounding the leads in see-through and with lead numbersincluded;

FIG. 2 is a top view of a first leadframe implementation;

FIG. 3 is a top view of a second leadframe implementation;

FIG. 4 is a top see-through view of the second leadframe implementationof FIG. 3 showing the outline of the lead surfaces that contact thecircuit board;

FIG. 5 is a top see-through view of the leadframe implementation of FIG.4 showing the outline of the finished package in dotted lines relativeto the leads;

FIG. 6 is a top see-through view of the leadframe implementation of FIG.4 showing the location of the chip and wire bonds coupling the chipconnections to the individual leads with the outline of the leads belowthe chip showing how the chip is supported mechanically by the leads.

DESCRIPTION

This disclosure, its aspects and implementations, are not limited to thespecific components, assembly procedures or method elements disclosedherein. Many additional components, assembly procedures and/or methodelements known in the art consistent with the intended leadframes willbecome apparent for use with particular implementations from thisdisclosure. Accordingly, for example, although particularimplementations are disclosed, such implementations and implementingcomponents may comprise any shape, size, style, type, model, version,measurement, concentration, material, quantity, method element, step,and/or the like as is known in the art for such leadframes, andimplementing components and methods, consistent with the intendedoperation and methods.

Referring to FIG. 1, an implementation of a conventional chip-on-leadpackage 2 is illustrated with the mold compound 4 surrounding the chip(silicon die) 6 (active side up) shown in dotted lines. As illustrated,the conventional chip-on-lead package includes a plurality of leads 6,8, 10 that extend into opening 12 and underneath (below) chip 6. Asillustrated by the dotted lines on the plurality of leads 6, 8, 10 thesurfaces of the leads that oppose, or are on the other side from, thechip 6 may be half etched to reduce their perimeter and size to theshape formed by the dotted lines. In this way, after packaging, the onlypart of the leads 6, 8, 10 that is exposed through the mold compound 4is the perimeter of the shape of each lead represented in dotted lines.This serves to reduce the exposed lead size and conserve space on thecircuit board to which the package 2 is coupled under the package 2. Ascan be observed, in the conventional package 2, each lead (pin) extendsbelow (underneath) the chip 6 when viewed from the top, mechanicallysupports the chip 6, and is mechanically coupled at the bottom surfaceof the chip (non-active side of the chip in various implementations).

Referring to FIG. 3, an implementation (second implementation) of aleadframe 14 is illustrated. As illustrated, the leadframe 14 includes aplurality of leads (pins 1-8), 16, 18, 20 which extend inwardly intoopening 22. As indicated by the continuation lines on all four sides ofthe leadframe 14, the material of the leadframe 14 continues out of theview of the picture during manufacturing and prior to trimming andseparating of the leads from the rest of the leadframe 14 at theconclusion of the package manufacturing process during packagesingulation. As illustrated in FIG. 3, one of the leads 24 does notextend into the opening 22 as far as the other leads (is shorter inlength than the rest). Furthermore, the lead 24 contains a thinnedportion 26, which has a thinner material thickness than the rest of thelead 24. In particular implementations the thinned portion 26 may behalf etched, or be substantially half of the thickness of the rest ofthe lead 24. In other implementations, where etching is not used tomanufacture the lead 24, it may be thinned using other techniques, suchas, by non-limiting example, molding, casting, cutting, and any othertechnique used to create a thinned portion 26 on the lead 24.

In various implementations, the lead 24 may be fully or partiallythinned along its length. Referring to FIG. 2, which is anotherimplementation (first implementation) of a leadframe 28, the lead 30 maynot include a thinned portion at all, but may be shorter in length thanthe lead 24 of the leadframe 14 illustrated in FIG. 3. Such animplementation may be manufactured through, by non-limiting example,fully etching, stamping, laser cutting, or otherwise singulating thelead 30. The reasons for this will be discussed hereafter.

Referring to FIG. 4, the outlines of the exposed surfaces 32, 34, 36 ofthe leads 16, 18, 20 are illustrated. These exposed surfaces 32, 34, 36represent the shape of the leads 16, 18, 20 as they appear on the bottomsurface of the package once the mold compound has be applied to theleadframe 14. As can be noted, the exposed surfaces 32, 34, 36 each havea perimeter bounded by the dotted line regions that merge with the solidline portions of each lead. These surfaces are smaller than the uppersurface of each of the leads. In various implementations these may becreated by half etching the exposed surfaces during manufacturing of theleadframe. In various implementations, particularly where the lead 24 isa thinned lead, the perimeter of the exposed surface 38 of the lead 24may be same in shape as one or more of the other leads 16, 18, 20. Thismeans that to the outside observer, in various implementations, once themolding compound has been applied, the fact that the lead 24 is shorterthan the other leads 16, 18, 20 is not visually apparent to the user.This also means that in various implementations, the exposed surface 38of the lead 24 may not be half etched as the rest of the lead are. Insuch implementations, no changes to PCB layouts may be required, becausethe bottom side of lead 24 has the same dimensions and position as therest of the leads (except for lead 1, which has different dimensions forthe purpose of identifying this pin during assembly with the PCB). Inother implementations, however, where the lead 24 does not have the sameshape and/or position as the rest of the leads a custom/altered PCBlayout could be used to accommodate it.

As illustrated in FIG. 2, however, in other implementations where thelead 30 is shorter than the size of the exposed surface 32, 34, 36 ofthe other leads illustrated in FIG. 1, the user will be able to visuallysee that the lead 30 has a different exposed perimeter and shape. Inother implementations, however, the leads 24, 30, whether thinned ornot, may also have a larger exposed surface than the other leads.

Referring to FIG. 5, the outline of the mold compound 40 over theleadframe 14 is illustrated, showing how the end of each lead will beflush with or slightly recessed within the outline of the mold compound40 after each package has been separated from the set of concurrentlymanufactured leadframes during processing.

Referring to FIG. 6, a semiconductor chip (die) 42 is shown coupled withthe leadframe 14. The coupling of the chip 42 with the leadframe 14takes place through a die bonding material (not shown) that is placedbetween the plurality of leads 16, 18, 20 and the surface of the chip 42that faces the plurality of leads (back surface). Also illustrated arevarious connectors/pad regions 44 on the chip 42 and wire bonds 46 thatelectrically couple the connectors 44 with the corresponding lead 20.The outlines of the plurality of leads 16, 18, 20 that extend under thechip 42 are illustrated in FIG. 6 in dotted lines.

It has been discovered that for a chip 42 that utilizes high voltage,the high voltage connectors 48 that are coupled to lead 24 are prone topremature failure over time as demonstrated during heated reliabilitypackage testing such as the High Temperature Operating Life (HTOL)reliability test. In various implementations, the die bonding materialis made of an epoxy material applied to the wafer containing the variouschips before the chips are diced. In this way, the die bonding materialis spread over the entire back surface of the die. In conventionalchip-on-lead packages like the one illustrated in FIG. 1, since all ofthe plurality of leads 6, 8, 10 extend beneath the chip 42 and aremechanically coupled at the back surface of the chip 42 through the diebonding material, those leads that handle high voltage relative to otherleads in the package (for example, in the range of about 100 V andhigher) are subject to failures and become a package reliability risk.Without being bound by any theory, it appears that over time the highvoltage isolation between lead and chip will fail, as demonstratedduring HTOL reliability testing as small air bubbles and small metalpieces in the chip bonding material create a conduction or breakdownpath and cause the bonding material to fail to isolate the applied highvoltage over an extended period of time.

By inspection in FIG. 6 it is apparent that the lead 24 does not extendbeneath the chip 42 and also, because of the presence of the thinnedportion 26, does not physically contact or become very close (relativelyspeaking) to physically contacting the back surface of the chip 42 (incomparison to the other leads). Because of this, there is no die bondingmaterial mechanically coupling the lead 24 at the back surface of chip42. As a result, the only mechanical coupling of the lead 24 with thechip 42 occurs through the mold compound which bridges the gap betweenthe lead 24 and the chip 42 during the molding process. Since the moldcompound bridging the gap has a much higher voltage isolation propertythan chip bonding materials that include epoxy, they generallydemonstrate much better long term reliability in the presence of highvoltage. Furthermore, the distance of the gap between the lead 24 andthe chip 42 is much larger than the about 10 to about 50 micron thicklayer of chip bonding material (in various implementations) separating alead bonded directly to the chip.

Because the lead 24 is not mechanically coupled at the back surface ofthe chip 42 through a die bonding material, and, indeed, is not locatedin relatively close proximity to the back surface of the chip 42, it canbe used to carry high voltage signals between the chip 42 and the lead24. This is because the lack of mechanical coupling and proximity to theback surface of the chip 42 prevents the negative effects from heatingfrom affecting a bond between the lead and the chip 42, as there is nodirect bond. Accordingly, the wire bonds handling high voltage signals50, bonded to the non-thinned section of the lead 24, allow the lead 24to handle high voltage signals without being affected by issues causedby failure of the bond between the lead 24 and the chip 42. In variousimplementations, because the lead 24 is not directly mechanicallycoupled to the chip 42 through a die bonding material, thecharacteristics of the mold compound used may be sufficient to preventany wire bond failures due to heating effects of the lead 24 during highvoltage operation.

While the lead 24 does not directly act to mechanically support the chip42, the remaining plurality of leads 16, 18, 20 may be more thansufficient to provide mechanical support. While in the figures a singlelead has been illustrated as having a shorter length and/or thinnedportion, more than one lead could be utilized that have either the same,a similar, or different lengths which are shorter than the rest of theplurality of leads. A wide variety of materials could be used for theleads and leadframe including, by non-limiting example, copper,aluminum, silver, various alloys, any combination of the same, and anyother electrically conductive material.

In places where the description above refers to particularimplementations of leadframes and implementing components,sub-components, methods and sub-methods, it should be readily apparentthat a number of modifications may be made without departing from thespirit thereof and that these implementations, implementing components,sub-components, methods and sub-methods may be applied to otherleadframes.

What is claimed is:
 1. A chip-on-lead package comprising: a leadframecoupled to a semiconductor chip, the leadframe comprising a plurality ofleads extending inwardly into an opening surrounded by the plurality ofleads; wherein at least one of the plurality of leads comprises athinned portion adjacent to the semiconductor chip and is an at leastone thinned lead; wherein the at least one thinned lead electricallycouples with a high voltage connector of the semiconductor chip; andwherein the plurality of leads, except for the at least one thinnedlead, mechanically couple to the semiconductor chip through a diebonding material.
 2. The package of claim 1, wherein the at least onethinned lead is configured to carry up to 200 volts.
 3. The package ofclaim 1, wherein the thinned portion of the at least one thinned lead isone of half etched and fully etched
 4. The package of claim 1, whereinthe plurality of leads is configured to couple with an electroniccircuit board at a surface of each of the plurality of leads oppositethe surface of the semiconductor chip.
 5. The package of claim 1,wherein the at least one thinned lead does not extend inwardly into theopening as far as the other leads of the plurality of leads.
 6. Thepackage of claim 1, wherein the plurality of leads is configured tomechanically support the semiconductor chip through coupling at thesurface of the semiconductor chip through a die bonding material.
 7. Thepackage of claim 1, wherein a perimeter of the surface of each of theplurality of leads opposite the surface of the semiconductor chip exceptfor the at least one thinned lead is smaller than a perimeter of asurface of each of the plurality of leads configured to be coupled atthe surface of the semiconductor chip.
 8. The package of claim 7,wherein the surface of each of the plurality of leads except for the atleast one thinned lead opposite the surface of the semiconductor chip ishalf etched.
 9. A chip-on-lead package comprising: a leadframe coupledto a semiconductor chip, the leadframe comprising a plurality of leadsextending inwardly into an opening surrounded by the plurality of leads;wherein at least one of the plurality of leads comprises a thinnedportion across a thickness of the lead and is an at least one thinnedlead; wherein the at least one thinned lead electrically couples with ahigh voltage connector of the semiconductor chip; and wherein theplurality of leads, except for the at least one thinned lead,mechanically couple to the semiconductor chip through a die bondingmaterial.
 10. The package of claim 9, wherein the at least one thinnedlead is configured to carry up to 200 volts.
 11. The package of claim 9,wherein the thinned portion of the at least one thinned lead is one ofhalf etched and fully etched
 12. The package of claim 9, wherein theplurality of leads is configured to couple with an electronic circuitboard at a surface of each of the plurality of leads opposite thesurface of the semiconductor chip.
 13. The package of claim 9, whereinthe at least one thinned lead does not extend inwardly into the openingas far as the other leads of the plurality of leads.
 14. The package ofclaim 9, wherein the plurality of leads is configured to mechanicallysupport the semiconductor chip through coupling at the surface of thesemiconductor chip through a die bonding material.
 15. The package ofclaim 9, wherein a perimeter of the surface of each of the plurality ofleads opposite the surface of the semiconductor chip except for the atleast one thinned lead is smaller than a perimeter of a surface of eachof the plurality of leads configured to be coupled at the surface of thesemiconductor chip.
 16. The package of claim 15, wherein the surface ofeach of the plurality of leads except for the at least one thinned leadopposite the surface of the semiconductor chip is half etched.
 17. Achip-on-lead package comprising: a leadframe coupled to a semiconductorchip, the leadframe comprising a plurality of leads extending inwardlyinto an opening surrounded by the plurality of leads; wherein at leastone of the plurality of leads comprises a thinned portion and is an atleast one thinned lead; wherein the at least one thinned leadelectrically couples with a high voltage connector of the semiconductorchip; and wherein the thinned lead is configured to not directlymechanically couple at the surface of the semiconductor chip.
 18. Thepackage of claim 17, wherein the at least one thinned lead is configuredto carry up to 200 volts.
 19. The package of claim 17, wherein thethinned portion of the at least one thinned lead is one of half etchedand fully etched
 20. The package of claim 17, wherein the plurality ofleads is configured to couple with an electronic circuit board at asurface of each of the plurality of leads opposite the surface of thesemiconductor chip.